Mevalonic acid products as mediators of cell proliferation in simian virus 40-transformed 3T3 cells.

Effects of treatment with serum-free medium and 25-hydroxycholesterol (25-OH) on the cell cycle of simian virus 40-transformed 3T3 fibroblasts, designated SV-3T3 cells, were studied and compared with simultaneous effects on the activity of 3-hydroxy-3-methylglutaryl (HMG) CoA reductase and incorporation of [3H]mevalonic acid into cholesterol, Coenzyme Q, and dolichol. The data confirm our previous finding (O. Larsson and A. Zetterberg, Cancer Res., 46: 1233-1239, 1986) that 25-OH inhibits the cell cycle traverse of SV-3T3 cells specifically in early G1. In contrast, treatment with serum-free medium had no effect on cell cycle progression. The effect of 25-OH on the cell cycle traverse was correlated to a substantial decrease in the activity of HMG CoA reductase, whereas there was no change in the rate of [3H]mevalonic acid incorporated into cholesterol, Coenzyme Q, and dolichol. When the cells were exposed to serum-free medium, there was no depression of activity of HMG CoA reductase, and the rate of [3H]mevalonic acid incorporated into dolichol and cholesterol was not affected in any appreciable degree. In contrast the rate of Coenzyme Q synthesis was substantially decreased as a result of serum depletion. A similar decrease in Coenzyme Q synthesis was also achieved by treating the cells with cholesterol-poor serum. This indicates that the rate of Coenzyme Q synthesis is dependent on the concentration of cholesterol in the culture medium. In order to analyze whether some of the products in the mevalonic acid biosynthetic pathway may be of importance in the control of G1 traverse and cell proliferation of SV-3T3 cells, cholesterol, Coenzyme Q, and dolichol were added as supplements to cells treated with 25-OH. It was shown that dolichol was capable of overcoming the 25-OH-induced inhibition of G1 traverse efficiently, whereas cholesterol and Coenzyme Q were considerably less effective. Considered together with the fact that the activity of HMG CoA reductase and incorporation of mevalonic acid into dolichol were unaffected following serum-free treatment, the results suggest that maintenance of a certain level of de novo synthesis of dolichol may contribute to the capability of SV-3T3 cells to proliferate in serum-free medium.